Reactions of an organoruthenium anticancer complex with 2-mercaptobenzanilide--a model for the active-site cysteine of protein tyrosine phosphatase 1B

The organometallic anticancer complex (η(6)-p-cymene)Ru(en)Cl]PF(6) (1, en = ethylenediamine) readily reacts with thiols and forms stable sulfenate/sulfinate adducts which may be important for its biological activity. Protein tyrosine phosphatase 1B (PTP1B), a therapeutic target, contains a catalytic cysteinyl thiol and is involved in the regulation of insulin signaling and the balance of protein tyrosine kinase activity. On oxidation, the catalytic Cys215 can form an unusual sulfenyl-amide intermediate which can subsequently be reduced by glutathione. Here we study reactions of 1 with 2-mercaptobenzanilide, 2, a recognized model for the active site of PTP1B. We have characterized crystallographically compound 2 and its oxidized sulfenyl-amide derivative 2-phenyl-1,2-benzisothiazol-3(2H)-one (4), which shows a close structural similarity to the sulfenyl-amide in oxidized PTP1B. At pH 7.4 and 5.3, 1 reacted with 2, affording a mono-ruthenium thiolato complex (η(6)-cym)Ru(en)(S-RS)](+) (7(+), R = (C(6)H(4))CONH(C(6)H(5))) and a triply-S-bridged thiolato complex ((η(6)-cym)Ru)(2)(μ-S-RS)(3)](+) (8(+)), respectively. Coordination of Ru to the S atom in 7 allows formation of a strong H-bond (2.02 ?) between the en-NH and the carbonyl oxygen. To assess the possible effect of ruthenium coordination on the redox regulation of PTP1B, reactions of these thiolato products with H(2)O(2) and/or GSH were then investigated, demonstrating that coordination to Ru largely retards both the oxidation (deactivation) of the thiol in compound 2 by H(2)O(2) and the subsequent reduction (reactivation) of the sulfenyl-amide by GSH, implying that the inhibition of complex 1 on PTP1B (IC(50) of 19 μM) may be attributed to coordination to its catalytic cysteine.